To reduce the overall size of an electronic device, a multi-chip module is applied. In the multi-chip module, a plurality of chips are mounted to a single substrate. Accordingly, the heat removal of the package of these chips becomes increasingly important to assure the proper operation. Using a common heat sink to dissipate heat generated from these chips is well known. However, during the operation, the chips may produce different heat. For some extreme cases, the heat difference between two chips can be as high as 10 times or above. Consequently, a heat sink with large cooling capability, which may be greater than the required cooling capability, is adopted to maintain good heat dissipation from all the chips. In addition, the thermal interference between or among the chips can be severe when the common heat sink is applied.